Tribological properties of PTFE‐filled PMIA

The polytetrafluoroethylene‐filled (PTFE) poly(m‐phenylene isophalamide) (PMIA) composite blocks are prepared by compression molding. The friction and wear of PTFE‐filled PMIA are investigated on a block‐on‐ring machine by running the PMIA composite block against plain carbon steel (AISI 1045 steel ring). The worn surface of PMIA composite and the steel counterface are examined by using electron probe microanalysis (EPMA). It is found that PTFE‐filled PMIA exhibited considerably lower friction coefficient and wear rate than pure PMIA. Furthermore, the lowest wear rate is obtained when the composite contains 20 vol % PTFE. EPMA investigations show that there are some debris that could restrain the wear of the PMIA composites oriented along the sliding track and embedded in the surface of PMIA composite. A kind of stripe transfer film that contains abundant F element should be the main reason for the improvement of the tribological properties of PTFE‐filled PMIA composites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 747–751, 1999     

Tribological behavior of micrometer‐ and nanometer‐Al2O3‐particle‐filled poly(phthalazine ether sulfone ketone) copolymer composites used as frictional materials

Micrometer‐ and nanometer‐Al₂O₃‐particle‐filled poly(phthalazine ether sulfone ketone) (PPESK) composites with filler volume fractions ranging from 1 to 12.5 vol % were prepared by hot compression molding. We evaluated the tribological behaviors of the PPESK composites with the block‐on‐ring test rig by sliding PPESK‐based composite blocks against a mild carbon steel ring under dry‐friction conditions. The effects of different temperatures on the wear rate of the PPESK composites were also investigated with a ball‐on‐disc test rig. The wear debris and the worn surfaces of the PPESK composites were investigated with scanning electron microscopy, and the structures of the PPESK composites were analyzed with IR spectra. The lowest wear rate, 7.31 × 10^?6 mm³ N^?1 m^?1, was obtained for the composite filled with 1 vol %‐nanometer Al₂O₃ particles. The composite with nanometer particles exhibited a higher friction coefficient (0.58–0.64) than unfilled PPESK (0.55). The wear rate of 1 vol %‐nanometer‐Al₂O₃‐particle‐filled PPESK was stable and was lower than that of unfilled PPESK from the ambient temperature to 270°C. We anticipate that 1 vol %‐nanometer‐Al₂O₃‐particle‐filled PPESK can be used as a good frictional material. We also found that micrometer‐Al₂O₃‐particle‐filled PPESK had a lower friction coefficient at a filler volume fraction below 5%. The filling of micrometer Al₂O₃ particles greatly increased the wear resistance of PPESK under filler volume fractions from 1 to 12.5%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 993–1001, 2005     

Tribological properties of SiO2 nanoparticle filled–phthalazine ether sulfone/phthalazine ether ketone (50/50 mol %) copolymer composites

SiO₂ nanoparticle filled–poly(phthalazine ether sulfone ketone) (PPESK) composites with various filler volume fractions were made by heating compression molding. The tribological behavior of the PPESK composites was investigated using a block‐on‐ring test rig by sliding PPESK‐based composite blocks against a mild carbon steel ring. The morphologies of the worn composite surfaces, wear debris, and the transferred films formed on the counterpart steel surface were examined with a scanning electron microscope, whereas the chemical state of the Fe element in the transfer film was analyzed with X‐ray photoelectron spectroscopy. In addition, IR spectra were taken to characterize the structure of wear debris and PPESK composites. It was found that SiO₂ nanoparticle filled–PPESK composites exhibit good wear resistance and friction‐reduction behavior. The friction and wear behavior of the composites was improved at a volume fraction between 4.2 and 14.5 vol % of the filler SiO₂. The results based on combined SEM, XPS, and IR techniques indicate that SiO₂ nanoparticle filled–PPESK composite is characterized by slight scuffing in dry sliding against steel and polishing action between composite surface and that of the countpart ring, whereas unfilled PPESK is characterized by severe plastic deformation and adhesion wear. In the former case a thin, but not complete, transfer film was formed on the surface of the counterpart steel, whereas in the latter case, a thick and lumpy transfer film was formed on the counterpart steel surface. This accounts for the different friction and wear behavior of unfilled PPESK and SiO₂ nanoparticle filled–PPESK composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2136–2144, 2002     

The tribological behavior of micrometer and nanometer TiO2 particle‐filled poly(phthalazine ether sulfone ketone) composites

Micrometer and nanometer TiO₂ particle‐filled poly(phthalazine ether sulfone ketone) (PPESK) composites with various filler volume fractions from 0.5 to 7.5 vol % were prepared by heating compression molding. The friction and wear behaviors of the PPESK composites were evaluated using the block‐on‐ring test rig by sliding PPESK‐based composite blocks against a mild carbon steel ring under dry friction conditions. The wear debris and the worn surfaces of the PPESK composites filled with micrometer and nanometer TiO₂ particles were investigated by using a scanning electron microscope (SEM), while the structures of PPESK composites and wear debris were analyzed with IR spectra. Experimental results show that antiwear properties of the PPESK composites can be improved greatly by filling nanometer TiO₂ particles, and the friction coefficient decreases when the filler volume fraction is below 2.5%, but when the filler volume fraction is above 2.5% the friction coefficient increases gradually with increasing filler volume fraction. In the case of micrometer TiO₂ filler, wear rates increase with increasing filler volume fractions under identical test conditions, and the friction coefficients are less sensitive to the filler volume fraction. It was also found that the wear mechanism of micrometer TiO₂ particle‐filled PPESK is mainly severe adhesion and abrasive wear, while that of nanometer TiO₂ particle‐filled PPESK is mainly slight abrasive wear. In the former case, there are no transfer film formed on the surface of the counterpart steel, and wear debris are in the form of long and large ribbon. While in the latter case, the wear debris was granule and their size was about 10 μm. In case of 1 vol % nanometer TiO₂ particle‐filled PPESK composites, the transfer film was fairly thinner and smoother, and the transfer film provided better coverage on the surface of steel ring, while that of 7.5 vol % was thicker and discrete. These account for the different friction and wear behavior of micrometer and nanometer TiO₂ particle‐filled PPESK composite. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 906–914, 2004     

Influence of solid lubricant reinforcement on wear behavior of Kevlar fabric composites

The friction and wear behavior of Kevlar fabric composites reinforced by PTFE or graphite powders was investigated using a Xuanwu‐III friction and wear tester at dry sliding condition, with the unfilled Kevlar fabric composite as a reference. The worn surfaces were analyzed by means of scanning electron microscope, and X‐ray photoelectron spectroscopy. It was found that PTFE or graphite as fillers could significantly improve the tribological behavior of the Kevlar fabric composites, and the Kevlar fabric composites filled with 20% PTFE exhibited the best antiwear and antifriction ability among all evaluated cases. The transfer films established with two lubricants in sliding wear of composites against metallic counterparts made contributions to reducing friction coefficient and wear rate of Kevlar fabric composites. In particular, FeF₂ generated in the sliding of Kevlar fabric composites filled with PTFE against counterpart pin improved the bonding strength between the transfer film and counterpart surface, which accounted for the lowest friction coefficient and wear rate of the Kevlar fabric composites filled with PTFE measured in the testing. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Effect of nanometer SiC filler on the tribological behavior of PEEK under distilled water lubrication

The composites of polyetheretherketone (PEEK) filled with nanometer SiC of different proportions were prepared by compression molding. The tribological behaviors of the composites under lubrication of distilled water were investigated and compared with that under dry sliding, on an M‐200 friction and wear test rig, by running a plain carbon steel (AISI 1045 steel) ring against the composite block. The worn surfaces of nanometer SiC filled‐PEEK and the transfer film were observed by means of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). As the results, nanometer SiC as the filler greatly improves the wear resistance of PEEK under dry sliding and distilled water lubrication, though the composites show different dependence of wear resistance on the filler content. Nanometer SiC‐filled PEEK showed signs of slight scuffing under distilled water lubrication, while a thin, uniform, and tenacious transfer film was formed on the surface of the counterpart steel ring. On the contrary, unfilled PEEK under lubrication of water showed signs of severe plowing and erosion, while the worn surface of the counterpart ring was very rough, and a discontinuous PEEK transfer film was formed. Thus, the different friction and wear behaviors of unfilled PEEK and nanometer SiC‐filled PEEK can be attributed to the different characteristics of the corresponding transfer films. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 609–614, 2000     

The tribological properties of SiC whisker-reinforced polyetheretherketone

SiC whisker-reinforced polyetheretherketone (PEEK) composites with different filler proportions were made into block specimens by compression molding. The friction and wear properties of the composites were investigated on a block-on-ring machine by running a plain carbon steel (AISI 1045 steel) ring against the composite block under ambient conditions. The morphologies of the wear traces and wear debris were observed by scanning electron microscopy (SEM). It was found that SiC whisker-reinforced PEEK exhibited considerably lower friction coefficient compared with pure PEEK, while SiC whisker as a filler at a content of 1.25 to 2.5 wt % was very effective in reducing the wear rate of PEEK. Especially, the lowest wear rate was obtained with the composite containing 1.25 wt % SiC whisker. The SEM pictures of the wear traces indicated that PEEK composites undertook abrasive wear that was enhanced with increasing SiC whisker content, while for the frictional couple of carbon steel ring/composite block (reinforced with 1.25 wt % filler), a thin, uniform, and tenacious transfer film was formed on the ring surface. It was also supposed that the differences in the content of SiC whisker as filler could cause the differences in the wear mechanisms of SiC whisker-reinforced PEEK composites. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2341–2347, 1998     

Tribological characteristics of nanometer Si3N4 filled poly(ether ether ketone) under distilled water lubrication

Nanometer Si₃N₄ filled poly(ether ether ketone) (PEEK) composite blocks with different filler proportions were prepared by compression molding. Their friction and wear properties under distilled water lubrication, as well as under ambient dry conditions, were investigated on a block on ring machine by running a plain carbon steel (AISI 1045 steel) ring against the PEEK composite block. The worn surfaces of nanometer Si₃N₄ filled PEEK and the transfer film were observed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The results showed that distilled water could reduce the friction coefficient of nanometer Si₃N₄ filled PEEK but with the sacrifice of a large reduction in wear resistance. The SEM and EPMA pictures of the worn surfaces indicated that the wear mechanisms of nanometer Si₃N₄ filled PEEK under distilled water lubrication and ambient dry rubbing conditions were different. Under water lubrication, the dominant wear mechanism of the filled PEEK was severe abrasive wear with surface fracture. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1394–1400, 2001     

Mechanical and tribological properties of glass–epoxy composites with and without graphite particulate filler

The objectives of this research article is to evaluate the mechanical and tribological properties of glass‐fiber‐reinforced epoxy (G–E) composites with and without graphite particulate filler. The laminates were fabricated by a dry hand layup technique. The mechanical properties, including tensile strength, tensile modulus, elongation at break, and surface hardness, were investigated in accordance with ASTM standards. From the experimental investigation, we found that the tensile strength and dimensional stability of the G–E composite increased with increasing graphite content. The effect of filler content (0–7.5 wt %) and sliding distance on the friction and wear behavior of the graphite‐filled G–E composite systems were studied. Also, conventional weighing, determination of the coefficient of friction, and examination of the worn surface morphological features by scanning electron microscopy (SEM) were done. A marginal increase in the coefficient of friction with sliding distance for the unfilled composites was noticed, but a slight reduction was noticed for the graphite‐filled composites. The 7.5% graphite‐filled G–E composite showed a lower friction coefficient for the sliding distances used. The wear loss of the composites decreased with increasing weight fraction of graphite filler and increased with increasing sliding distance. Failure mechanisms of the worn surfaces of the filled composites were established with SEM. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2472–2480, 2007     

The mechanical and tribological properties of PTFE filled with PTFE waste powders

Polytetrafluoroethylene (PTFE) composites filled with PTFE waste offer interesting combination of tribological properties and low cost. PTFE composites waste was mechanically cut and sieved into powders. PTFE composites filled with PTFE waste powders were prepared by compression molding. Friction and wear experiments were carried out in a reciprocating sliding tribotester at a reciprocating frequency of 1.0 Hz, a contact pressure of 5.5 MPa, and a relative humidity of (60 ± 5)%. PTFE materials slid against a 45 carbon steel track. Results showed that a PTFE composite (B) filled with 20 wt % PTFE waste exhibited a coefficient of steady‐state friction slightly higher than that of unfilled PTFE (A), while wear resistance over two orders of magnitude higher than that of unfilled PTFE (A). Another PTFE composite filled with PTFE waste and alumina nanoparticles exhibited the highest wear resistance among the three PTFE materials. This behavior originates from the effective reinforcement of PTFE waste as a filler. It was experimentally confirmed that the low cost recycling of PTFE waste without by‐products is feasible. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1035–1041, 2007     

Friction and wear behavior of basalt‐fabric‐reinforced/solid‐lubricant‐filled phenolic composites

To improve the tribological properties of basalt‐fabric‐reinforced phenolic composites, solid lubricants of MoS₂ and graphite were incorporated, and the tribological properties of the resulting basalt‐fabric composites were investigated on a model ring‐on‐block test rig under dry sliding conditions. The effects of the filler content, load, and sliding time on the tribological behavior of the basalt‐fabric composites were systematically examined. The morphologies of the worn surfaces and transfer films formed on the counterpart steel rings were analyzed by means of scanning electron microscopy. The experimental results reveal that the incorporation of MoS₂ significantly decreased the friction coefficient, whereas the inclusion of graphite improved the wear resistance remarkably. The results also indicate that the filled basalt‐fabric composites seemed to be more suitable for friction materials serving under higher loads. The transfer films formed on the counterpart surfaces during the friction process made contributions to the reduction of the friction coefficient and wear rate of the basalt‐fabric composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of lubricating‐oil additives on the friction and wear properties of polymers and their composites sliding against steel under oil‐lubricated conditions

The effects of lubricating‐oil additive zinc dialkyldithiophosphate (ZDDP) on the friction and wear properties of polymers and their composites sliding against GCr15 bearing steel were studied by using an MHK‐500 ring‐on‐block wear tester (Timken wear tester). Then the frictional surfaces of the friction pairs were examined by using electron probe microanalysis (EPMA). Experimental results show that the ZDDP contained in liquid paraffin has little effect on the friction coefficients of the polyimide (PI) or polyamide 66 (PA66) against GCr15 bearing steel friction pairs compared with that under the lubrication of liquid paraffin, but it slightly reduces the friction coefficients of polytetrafluoroethylene (PTFE) or its composites against GCr15 bearing steel friction pairs. Under lubrication of liquid paraffin containing 2 wt % ZDDP, the ZDDP film absorbed on the frictional surfaces of the PTFE composites–GCr15 bearing steel friction pairs exhibits obvious antiwear properties; it greatly reduces the wear of pure PTFE and the PTFE composites filled with Pb, PbO, and MoS₂; and the wear of the PTFE composites can be reduced by one order of magnitude compared with that under lubrication of pure liquid paraffin. Meanwhile, the inorganic fillers Pb, PbO, and MoS₂ contained in PTFE have little effect on the absorption of ZDDP to the frictional surfaces, so they have little effect on the friction coefficients of the PTFE composites–GCr15 bearing steel friction pairs under the lubrication of liquid paraffin containing 2 wt % ZDDP. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1240–1247, 2000     

Investigations of the tribological properties of carbon fabric reinforced phenolic polymer composites filled with several nanoparticles

The carbon fabric composites filled with several nanoparticles were prepared by dip‐coating and hot press molding technique. The friction and wear behavior of the resulting composites were studied systematically using a block‐on‐ring arrangement. Experimental results showed that the optimal content of nanoparticles as fillers contributed to improve the tribological properties of the carbon fabric composites. Moreover, the friction and wear properties of the fabric composites were closely dependent with the sliding conditions. The differences in the transfer film formed on the counterpart surface during the friction process also accounted for the friction and wear behavior of carbon fabric composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Tribological behavior of the polyamide composite coating filled with different fillers under dry sliding

The polyamide (PA) composite coating filled with the particles of microsized MoS₂, microsized graphite, and nano‐Al₂O₃, respectively, were prepared by flame spraying. The friction and wear characteristics of the PA coating and composite coating filled with the varied content of filler under dry sliding against stainless steel were comparatively investigated using a block‐ring tester. The morphologies of the worn surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. The result showed that the addition of fillers to the composite coatings changed significantly the friction coefficient and wear rate of the coatings. The composite coatings filled with a low level content of fillers showed lower wear rate than did pure PA coating under dry sliding; especially the MoS₂/PA composite coating had the lowest wear rate among these composite coatings. The composite coatings with a high level content of fillers had higher wear rate than did pure PA coating, except of the Al₂O₃/PA composite coating. The bonding strengths between the polymer matrix and fillers changed with the content of the fillers, which accounted for the differences in the tribological properties of the composite coatings filled with the varied content fillers. On the other hand, the difference in the friction and wear behaviors of the composite coatings and pure coating were attributed to the difference in their worn surface morphologies and transfer film characteristics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Friction and wear properties of basalt fiber reinforced/solid lubricants filled polyimide composites under different sliding conditions

Short basalt fibers (BFs)‐reinforced polyimide (PI) composites filled with MoS₂ and graphite were fabricated by means of hot‐press molding technique. The tribological properties of the resulting composites sliding against GCr15 steel ring were investigated on a model ring‐on‐block test rig. The wear mechanisms were also comparatively discussed, based on scanning electron microscopic examination of the worn surface of the PI composites and the transfer film formed on the counterpart. Experimental results revealed that MoS₂ and graphite as fillers significantly improved the wear resistance of the BFs‐reinforced polyimide (BFs/PI) composites. For the best combination of friction coefficient and wear rate, the optimal volume content of MoS₂ and graphite in the composites appears to be 40 and 35%, respectively. It was also found that the tribological properties of the filled BFs/PI composites were closely related with the sliding conditions such as sliding speed and applied load. Research results show that the BF/PI composites exhibited better tribological properties under higher PV product. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Tribological properties of micro‐ and nanoparticles‐filled poly(etherimide) composites

It has been found that nano‐ or microsized inorganic particles in general enhance the tribological properties of polymer materials. In the present study, 5 vol % nano‐TiO₂ or micro‐CaSiO₃ was introduced into a polyetherimide (PEI) matrix composite, which was filled additionally with short carbon fibers (SCF) and graphite flakes. The influence of these inorganic particles on the sliding behavior was investigated with a pin‐on‐disc testing rig at room temperature and 150°C. Experimental results showed that both particles could reduce the wear rate and the frictional coefficient (μ) of the PEI composites under the applied testing conditions. At room temperature, the microparticles‐filled composites exhibited a lower wear rate and μ, while the nano‐TiO₂‐filled composites possessed the lowest wear rate and μ at elevated temperature. Enhancement in tribological properties with the addition of the nano‐particles was attributed to the formation of transfer layers on both sliding surfaces together with the reinforcing effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1678–1686, 2006     

Enhanced tribological performance of hybrid polytetrafluoroethylene/Kevlar fabric composite filled with milled pitch‐based carbon fibers

As self‐lubricating bearing liner materials, tribological properties of milled pitch‐based carbon fibers (CFs) modified polytetrafluoroethylene (PTFE)/Kevlar fabric composites were investigated, and the microscopic morphology of worn surface was studied. The results show that the appropriate incorporation of CFs can obviously reduce the wear rate of the fabric composite with almost unchanging friction coefficient. The wear rates of 5 wt % CF‐filled PTFE/Kevlar fabric composites are decreased by 30% and 48% for two kinds of composites made with fibers from different producers compared with unfilled fabric composites. Scanning electron microscopy observations show that the appropriate incorporation of CFs obviously improves the interfacial bonding and reduces pull‐out and fracture of Kevlar fiber. Meanwhile, the introduction of CFs at proper fraction is helpful to form smooth and continuous transfer film on the surface of metal counterpart. The improving mechanism of the CF is attributed to increasing mechanical strength, thermal conductivity and self‐lubricating effects. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46269.     

Tribological properties of bismaleimide composites with surface‐modified SiO2 nanoparticles

In this article, the surface of SiO₂ nanoparticles was modified by silane coupling agent N‐(2‐aminoethyl)‐γ‐aminopropylmethyl dimethoxy silane. The bismaleimide nanocomposites with surface‐modified SiO₂ nanoparticles or unmodified SiO₂ nanoparticles were prepared by the same casting method. The tribological performance of the nanocomposites was studied on an M‐200 friction and wear tester. The results indicated that the addition of SiO₂ nanoparticles could decrease the frictional coefficient and the wear rate of the composites. The nanocomposites with surface‐modified SiO₂ nanoparticles showed better wear resistance and lower frictional coefficient than that with the unmodified nanoparticles SiO₂. The specific wear rate and the steady frictional coefficient of the composite with 1.0 wt % surface‐modified SiO₂ nanoparticles are only 1.8 × 10^?6 mm³/N m and 0.21, respectively. The dispersion of surface‐modified SiO₂ nanoparticles in resin matrix was observed with transmission electron microscope, and the worn surfaces of pure resin matrix and the nanocomposites were observed with scanning electron microscope. The different tribological behavior of the resin matrix and the filled composites should be dependent on their different mechanical properties and wear mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tribological behavior of Kevlar fabric composites filled with nanoparticles

The friction and wear characteristics of ZnO‐ or montmorillonite‐nanoparticle‐filled Kevlar fabric composites with different filler proportions when sliding against stainless steel pins under dry friction conditions were studied, with unfilled Kevlar fabric composites used as references. The worn surface and transfer film of Kevlar fabric composites were then examined with a scanning electron microscope. It was found that ZnO and montmorillonite as fillers could improve the tribological behavior of the Kevlar fabric composites with various applied loads, and the best antiwear property was obtained with the composites containing 5 wt % ZnO or montmorillonite. This indicated that these nanoparticles could prevent the destruction of Kevlar fabric composites during the friction process. The transfer film established by these nanoparticles during the sliding wear of the composites against their metallic counterpart made contributions to reducing the friction coefficient and wear rate of the Kevlar fabric composites measured in the test. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanism of filler action in reducing the wear of PTFE polymer by differential scanning calorimetry

Two types of representative nanometer materials, i.e., fibroid nanometer attapulgite and approximate spherical ultrafine diamond, were selected as fillers of polytetrafluoroethylene (PTFE) to study the mechanism of the wear‐reducing actions of the fillers in PTFE composites. The friction and wear tests were performed on a block‐on‐ring wear tester under dry sliding conditions. Differential scanning calorimetry (DSC) was used to investigate material microstructure and to examine modes of failure. No significant change in coefficient of friction was found, but the wear rate of PTFE composites was orders of magnitude less than that of pure PTFE. DSC analysis revealed that nanometer attapulgite and ultrafine diamond played a heterogeneous nucleation role in PTFE matrix and consequently resulted in increasing the crystallinity of PTFE composites. Moreover, the PTFE composite with higher heat absorption capacity and crystallinity exhibited improved wear resistance. A propositional “sea‐frusta” frictional model explained the wear mechanism of filler action in reducing the wear of PTFE polymer, i.e., fillers in the PTFE matrix effectively reduced the size of frictional broken units for PTFE composites and restrained the flowability of the units, as well as supporting the applied load. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007